1. Field of the Invention
The present invention relates to apparatus in flow distribution device(s) for reducing the force necessary for opening or closing other apparatus subject to fluid pressure differentials and flow created forces, while simultaneously reducing the potential for oscillation and/or pressure pulsations or ripples at the metering element, including reduced metering edge wear; and more particularly relates to apparatus for reducing the amount of force necessary to open and close off fluid flow in various fluid flow arrangements, particularly in devices with valve like function arrangements.
2. Background of the Invention
Numerous attempts have been made in the past to facilitate the opening and closing of various valve arrangements to increase the flow conditions of the valve. Some of those attempts have merely been to increase the energy put into the valve actuating mechanism by, for example, increasing the current through an actuating solenoid. Other attempts to reduce the force necessary for such opening or closing have been exhibited in such activities of Hayner in U.S. Pat. No. 4,325,412 by centering the valve spool in the valve sleeve and to the employment of an “anti flow device” to reduce spool actuating forces.
As discussed in Section 5.6 of “Hydraulic Control Systems” Herbert E. Merritt, John Wiley & Sons, 1967, flow forces on spool valves are generally referred to as “flow induced forces”, “Bernoulli forces”, or “hydraulic reaction forces.” Other writers have referred to these forces as “error forces”, i.e. forces that are caused by the structure and function of the valve which were not generally intended, and result in the necessity of increased opening and closing forces on the valve. However, all of these names are applied to those forces which act upon a valve as a result of fluid flowing in the valve chambers and through the valve openings or orifices.
Other techniques covered by P. Hayner in U.S. Pat. No. 4,325,412 & R. Mickelson in U.S. Pat. No. 6,397,890 all have attempted to reduce such forces. However, the Series & Parallel passages suggested in Hayner while including a circumferential balancing of the valve spool for centering purposes, does not include using the centering passages as part of the series fluid bleed passages represented by the force reducing geometry of the present invention. Moreover, Staggered holes, & or notches of various geometries in similar manner to the R. Mickelson patent, have been utilized, but none of these utilize series incremental pressure drop passages which are employed as a feature of the present invention. As shall be more completely recognized in the following discussion, the present invention includes series and/or parallel feed and/or bleed passages. In the convention of hydraulics, “feed” means a flow from a “source” to “work port” (intermediate pressure) and “bleed” means from “source” or “work port” to “tank”. However, hereinafter the term “bleed” shall be used generically to merely refer to a passage from a higher pressure to a lower pressure.
Staggered hole & flow force compensation techniques have been outlined in Textbook Sections 4.3.1 & 4.3.2. of “The Control of Fluid Power” D. McCloy, H. R. Martin, Longman Group LTD. London, 1973; and Section 10.321 of “Fluid Power Control” J. F. Blackburn, J. L. Coakley, F. D. Ezekiel, M.I.T. Press, 1960. Particularly, Parallel passages are described within section 4.3.1 of the McCloy text but again this technique does not utilize series incremental pressure drop passages.